1. Field of the Invention
The present invention relates to a preparation method of a phosphaphenanthrene-based compound, and more particularly, to a phosphaphenanthrene-based compound applicable to copper-clad laminates (CCL) and printed circuit boards and related preparation method.
2. Description of the Prior Art
Printed circuit boards are widely used in various applications, such as large-scale industrial computers, communication devices, electrical measurements, national defense and aviation products, and consumer electronic products. As technology advances, various electronic products are designed to be miniaturized and multi-functional and have high performance and high reliability. Accordingly, the design and development of printed circuit boards tend to high precision, high density, and high performance and to be micro-porous, thinned and multi-layered.
A reflow process (such as IR-reflow) is required for mounting the surface components (such as active components or passive components) on the printed circuit boards, such that the lead-free solders are melted to connect the surface components with the metal lines on the printed circuit boards. Generally, the resin material constituted the insulating layer of the printed circuit boards is easily deformed after suffering heat impact of the reflow process due to different coefficients of thermal expansion. Accordingly, the laminate is warped and deformed and the flatness of the laminate is decreased, thereby problems of poor welding (e.g., nonwetting or false soldering) occur. Since the calorific power increases as the density of the interconnection of the printed circuit board becomes higher, to reduce the coefficient of thermal expansion of the insulating layer is an important topic to be addressed and discussed.
Take the epoxy resin composition as an example for the material of the printed circuit boards, various flame retardants (e.g., halogen flame retardants and phosphorus-containing flame retardants) have been used to provide a suitable flame retardancy for the material. Among them, the halogen flame retardants are forbidden due to environmental issues, while the applications of the phosphorus-containing flame retardants, e.g., phosphate ester (Taiwan Patent No. 1238846) and red phosphorus (Taiwan Patent No. 322507) are limited. The reason is that the hydrolysis reaction of the phosphate ester would generate acid which affects the migration resistance of the phosphate ester, and small quantities of phosphine gas would be produced when the red phosphorus is in a hot and humid environment, thereby the red phosphorus is considered dangerous. Accordingly, the application of the above two kinds of phosphorus-containing flame retardants are limited.
In addition, the conventional phosphazene compound (e.g., SPB-100 produced by Otsuka Chemical) has no functional groups, and therefore the conventional phosphazene compound added to the halogen-free resin composition may not be able to react and bond with other resins. Furthermore, the melting point of the condensed phosphate ester (PX-200) is low and the migration of the condensed phosphate ester is too high at high temperature. Accordingly, the coefficient of thermal expansion of the laminate manufactured from the resin composition is large such that inner cracking are caused during the manufacturing process of the circuit boards and the process yield is reduced.
Consequently, the phosphaphenanthrene-based compound and its derivatives become important due to their molecular structure containing phosphorus atom, biphenyl ring, and phenanthrene ring. Among them, though the hydroxyl group in 2-(10H-9-oxa-10-phospha-1-phenanthryl)hydroquinone phosphorus oxide (DOPO-HQ) may react and bond with other resins, the hydroxyl group would have negative impact on the dielectric constant and the dissipation factor, wherein the dielectric constant of the copper-free laminate (the resin content is about 55%) measured at 10 GHz is higher than 4.0 and the dissipation factor of the copper-free laminate at 10 GHz is higher than 0.010. Accordingly, it is still not suitable to add the phosphaphenanthrene-based compound having the hydroxyl group into the resin composition since it's difficult for the resin composition with the phosphaphenanthrene-based compound to have low dielectric property.